Concrete slabs are ubiquitous in today's world. From highways to airport runways to parking lots to building floors, sidewalks, and driveways, concrete slabs form the durable surfaces we depend on for modem life. The methods used to construct all these differing structures are essentially the same in that they all require that the wet concrete mixture be poured into a form and a mechanism by which the concrete can be leveled and compacted.
In its simplest form, this process is accomplished by the use of wooden forms, most commonly 2 by 6 or 2 by 8 material, that is positioned in a parallel manner at the desired width. This form then operates to contain the poured concrete in a lateral area that is to be covered by the concrete slab. When the required amount of concrete is thus positioned, it is then necessary to level it off to the height of the forms. It is this later process in which the screed is employed. In this method the leveling process is accomplished by moving a flat piece of material spanning the two parallel forms in a back and forth manner. This operation serves to move any of the excess concrete that extends above the upper surfaces of the forms either into any low areas or off of the prospective slab altogether.
While the manual method described above works well enough on small jobs such as the repair of short sections of sidewalk, it has numerous deficiencies. The first of these is, that even in small jobs, it is labor intensive and therefore costly over the long term. Additionally, the use of a manual screed is not very effective at distributing and compacting the concrete within the form therefore producing a finished slab of a lesser quality than is generally desired. More importantly, the manual screed is effectively useless in larger jobs where wide slabs of concrete are required.
Many of the problems associated with the use of manual screeds have been solved by the use of powered models. The power screeds available today come in two general forms. The first of these generally consist of a flat screed bar that is attached to a motorized articulation apparatus. In use, the screed bar fits over existing forms in much the same manner as the manually operated screed. The screed bar is then moved back and forth over the concrete by the articulation motor. While this system solves some of the problems associated with screeds, especially in larger jobs, it is cumbersome both in construction and operation.
The other type of powered screed is referred to as a powered roller screed. The powered roller screed generally consists of an elongated tube that is rotationally driven by an attached motor. In operation, the roller tube is positioned over the raw concrete at a position on the upper edges of the forms. The roller tube is then moved along the top of the forms in a direction that is opposite the rotational motion of the roller tube at its point of contact with the concrete. This apparatus produces a smooth and flat finish to the concrete and is generally considered to be the preferred method in the industry today.
While the powered roller screeds described above are effective, they do suffer from a number of operational deficiencies. The first of these is that they are designed and built in fixed lengths and are therefore not adjustable to accommodate concrete pours of varying widths. While this is not a huge problem, it results in the use of screed apparatuses that extend well over the forms making them difficult to maneuver at the job site.
Another problem with the powered roller screeds of the prior art is that they offer no way to compensate for special application concrete pours. It is often desirable to pour a concrete slab that either has a ridge or valley running longitudinally through its center. This form of concrete slabs is an effective way of controlling water with respect to the surface of the slab. The prior art consists entirely of screed apparatuses that have rigid rolling tubes. Therefore, in the past the only way of constructing ridges or valleys in concrete slabs was to pour each side of the slab independently. While this method works, it is more time consuming than it would be to perform the entire pour in one pass.
A further problem existing in the prior art is that they provide no reasonable means by which an extremely wide concrete pour can be accomplished as a single operation. This problem arises because the power sources are not powerful enough to drive long sections of screed roller tubes. A possible solution to this is to place a power unit on either side of the roller tube. For this approach to work, however, the power units must be capable of operating in opposite directions and their rate of rotation must be matched exactly. While possible, these requirements of such an apparatus make it impractical to build and operate such an apparatus.
A still further problem in the prior art is the inability of screed apparatuses to operate effectively in construction circumstances that require a circular concrete slab. Circular concrete slabs are commonly used in the construction of grain silos and other similar buildings. In the past the only way to finish these types of slabs was to run a screed apparatus over the pour from one end to the other or to manually rotate it around the pour. These methods work but produce results that are less than desirable.
From the forgoing discussion it can be seen that is would be desirable to provide a screed apparatus that is easily adjustable in the length of its roller thereby allowing it to be fitted to specific job applications. Additionally, it can be seen that it would be desirable to provide a screed apparatus that is capable of flexing to accommodate concrete pours containing ridges or valleys. It can also be seen that it would be desirable to provide a screed apparatus that is capable of operating in extremely wide concrete pours. Finally, it can be seen that it would be desirable to provide a screed apparatus that can be operated effectively in the finishing of circular concrete slabs.